1. Field of the Invention
The present invention relates generally to the field of injectors for internal combustion engines. More particularly, the invention relates to a novel geometry for a nozzle and poppet arrangement in an injector, particularly well suited for single fluid, pressure surge, direct in-cylinder fuel injection.
2. Description of the Related Art
In the field of internal combustion engines, various structures have been proposed over the years and are presently in use for providing the desired mix of fuel and gas, typically air, in combustion cylinders. In a particularly useful family of structures, an injector is fed with fuel and expresses fuel directly into a combustion chamber in a measured and properly timed sequence. The fuel is atomized upon injection into the chamber and is rapidly ignited by a spark plug to provide the rapid expansion needed to drive the engine.
It has been found that the performance of internal combustion engines may be substantially affected by the quality and characteristics of the atomization or spray provided by such injectors. In conventional injector structures, a central poppet or pintel is opened and closed within an injector nozzle body with each engine cycle, to introduce the desired quantity of fuel or fuel and gas mixture. When the poppet is displaced with respect to the body, a passageway is opened in an annular region between the poppet and a bore within the injector nozzle. Fuel flows through the passageway and enters into the combustion chamber where it is ignited. Prior to ignition, the poppet is withdrawn to its seating position within the bore to isolate the fuel feed from the combustion taking place in the chamber.
A wide variety of poppet-type fuel injectors have been developed to provide the desired sealing and flow of fuel into internal combustion engines. In general, the poppet may seat within the injector nozzle body at a position removed from the front or external surface of the body. The surfaces between the outer portion of the poppet and the injector nozzle body may take on various geometries, depending upon the desired fuel spray distribution, combustion properties, the strategy for cleansing the poppet and housing, and so forth. Alternatively, the poppet may be provided with a seating surface which contacts the injector body bore at some intermediate position between the tip of the poppet and more internal surfaces. Finally, injectors have been developed in which a poppet seats at a tip or toe located at or closely adjacent to the end of the poppet, where the poppet exits from the injector body during opening.
The various injector configurations heretofore proposed have advantages and drawbacks depending upon their particular application. For example, applications in which fuel is injected in a vapor or air carrier may be considerably different from those in which liquid fuel is conducted through the injector to the combustion chamber. In the former case, atomization of the fuel is performed prior to channeling of the fuel through the injectors. In the latter case, however, atomization occurs at the point of injection in the combustion chamber. The particular geometry of the injector nozzle body and poppet may be of considerable importance in obtaining good atomization in fuel injectors, particularly in systems in which the atomization is performed at the point of injection. However, heretofore known structures have not provided the most optimal atomization. Indeed, existing structures tend to cause inconsistent atomization, or insufficient breakdown of the fuel into a fine mist or spray as a result of the injector structure.
There is a need, therefore, for an improved fuel injector which overcomes these drawbacks of prior art devices. There is a particular need for an injector capable of reliably producing a fine spray or mist directly in a combustion chamber. Moreover, there is presently a need for such an injector structure which is robust to manufacturing variations and can be economically manufactured and installed in existing engine designs.
The invention provides a novel injector structure designed to respond to these needs. The injector is particularly well suited for applications in which liquid fuel is delivered to the injector tip where it is atomized directly into an engine combustion chamber. The injector may be driven in a variety of manners, such as by pulses in single fluid, pressure surge, direct in-cylinder fuel injection systems. The injector structure includes a nozzle body having a fuel flow bore, and a poppet or a pintel positioned within the bore. The region of the bore near the injector forms a flow controlling surface, with a corresponding surface being provided on the poppet. An annular region formed between the bore and the poppet serves to store a reservoir of fuel. Generally conforming surfaces of the poppet and bore, immediately adjacent to the injector tip, seat within one another to prohibit the ingress of combustion products and the outflow of fuel into the combustion chamber, when the injector is closed. The poppet is displaceable to an injection or flow position wherein the flow controlling surfaces adjacent to the injector tip direct or channel fuel to the injector tip, accelerating the fuel as it approaches the combustion chamber. The surfaces of the body and the poppet at the injector tip form a sharp-edged orifice promoting excellent atomization of the liquid fuel as it enters the combustion chamber. The body and poppet are machined to produce a planar surface. The surface of the poppet being formed so that after the poppet is machined, sufficient surface remains to properly direct fuel into the combustion chamber.
The invention also provides a novel method for forming an injector assembly. The method permits the formation of the various subcomponents of the assembly prior to assembly of the poppet and related structures in the injector nozzle body. Thereafter, the injector assembly is processed to form a flush tip surface with the front surface of the poppet extending in a common plane with the valve body, generally perpendicular to the central axis of the poppet. The surface of the poppet being formed so that after the poppet is machined, sufficient surface remains to properly direct fuel into the combustion chamber. The poppet and valve body seat is defined beginning at the plane and extending rearwardly into the valve body. The method permits the economical manufacture of injectors capable of providing superior atomization of liquid fuels by virtue of the creation of a sharp-edged orifice at the injector tip.